An extruded AZ80 Mg alloy was subjected to ECAP and subsequent artificial ageing to investigate the influences of ECAP passes and ageing conditions on the mechanical properties. The microstructures and mechanical properties were characterized by optical microscopy (OM), scanning electronic microscopy (SEM) and uniaxial tension tests. The static toughness values were calculated to evaluate the combined effects of ECAP and artificial ageing on the toughness. It is indicated that combination of ECAP and ageing at 300oC for 8h can significantly increase the toughness of as-extruded AZ80 alloy by 43%. The remarkable twinning and uniform dimples due to the continuous precipitation should be responsible for the increased tensile toughness.